BackgroundRisk factors for perinatal posttraumatic stress disorder (PTSD) among parents of an infant in the NICU have varied in previous literature. The relationships between perception of illness severity and objective measures of illness severity with PTSD are not well understood. AimsTo determine if PTSD among parents after an infant NICU discharge can be predicted by 1) objective measures of infant illness severity or 2) perceptions of infant illness severity. Study designA prospective, observational study. SubjectsParent/infant dyads who were in the NICU for ≥14 days. Outcome measuresObjective measures of illness severity were obtained from the electronic health record. Perceptions of illness were measured by the response to the question, “How sick is your child/patient?” on a 5-point Likert scale. The Perinatal Post-Traumatic Stress Disorder Questionnaire (PPQ) was completed by parents three months after discharge. ResultsOne hundred ninety-four dyads participated in the study, 86% of parents completed follow up screening. 25% of parents screened positive for PTSD. Parents perceived infants to be sick more often than hospital caregivers. In bivariate analysis many objective measures of illness severity were associated with PTSD. Parent perceptions of illness were also associated with PTSD after adjusting for objective measures of illness (OR 3.2, 95% CI 1.1–6.1, p = 0.008). ConclusionsPTSD in parents after NICU discharge is multifactorial. Objective illness risk factors can be used to screen parents at risk. Hospital caregivers should strive to understand parents' perception of illness and improve communication to potentially decrease PTSD after discharge.